MS-DOS was originally developed by Tim Paterson of Seattle Computer Products in 1980. At the time, Microsoft was providing the BASIC language interpreter for IBM, and was asked by the company to develop an operating system.

According to The Next Web, Microsoft hired Paterson in 1981 and bought his 86-DOS system for $75,000, renaming it MS-DOS. Microsoft Word for DOS was released shortly after in 1983 and was designed to be used with a mouse. It wasn't until 1989, however, that the world experienced Word for Windows — a juggernaut success that made Microsoft the king of the PC industry. Four years later, it was generating over half the revenue of the worldwide word-processing market.

"For more than a year, 35 of Microsoft's staff of 100 worked fulltime (and plenty of overtime) on the IBM project," Bill Gates told PC magazine for their inaugural issue in the early '80s, just after the launch of the IBM PC. "Bulky packages containing computer gear and other goodies were air-expressed almost daily between the Boca Raton [IBM] laboratory and Seattle [Microsoft]. An electronic message system was established and there was almost always someone flying the arduous 4,000 mile commute."

Fast forward three decades, and today there are over 1 billion people using Microsoft Office.

"Great things come from modest beginnings, and the great Microsoft devices and services of the future will probably start small, just as MS-DOS and Word for Windows did," Managing Director of Microsoft Research Roy Levin wrote.